Quinone transfer radical polymerization of styrene catalyzed by metal complexes in the presence of various o-quinones

Several o-quinones have been tested as control agents for the quinone transfer radical polymerization (QTRP) of styrene in the presence of cobalt(II) acetylacetonate. In contrast to the commercially available 3,5-di-tert-butyl-o-benzoquinone (3,5-DtBBQ) and tetrachloro-1,2-benzoquinone (tetrachloro-1,2-BQ), 3,6-dimethoxy-9,10-phenanthrenequinone (3,6-DMPhQ) imparts a better control to the radical polymerization of styrene compared to 9,10-phenanthrenequinone (PhQ) used as a reference. Indeed, whenever 3,6-DMPhQ is added with a catalytic amount of metal complexes (Co(acac)(2) or Al(acac)(3)), the evolution of the molar mass with the monomer conversion is linear, and low polydispersity (M-w/M-n similar to 1.1-1.2) is observed until very high monomer conversion (similar to 90%). Finally, the methoxy protons of 3,6-DMPhQ have been detected by H-1 NMR analysis of the polystyrene end groups, which is important mechanistic information.